JP2023032782A - Titanium nail and titanium material - Google Patents

Abstract

To provide a titanium nail having excellent bending resistance and wear resistance, and a titanium material used as a material therefor.SOLUTION: A titanium nail is composed of industrial pure titanium or titanium alloy and comprises a cured layer from its surface to a depth of at least 100 μm. The difference between a Vickers hardness HVS at a position of 100 μm from the surface in the depth direction and a Vickers hardness HVB at a position of 1000 μm from the surface in the depth direction satisfies the following formula (i): 30≤HVS-HVB≤200.SELECTED DRAWING: None

Description

The present invention relates to titanium nails and titanium materials.

2. Description of the Related Art Conventionally, nails are used to join members together in the construction of houses and the like. Iron nails are commonly used.

In addition, Japanese nails made of iron have long been used in wooden buildings designated as important cultural properties and national treasures of Japan. When a wooden building such as an important cultural property is renovated, the Japanese nails used for the renovation are often reused after being pulled out. Therefore, Japanese nails in particular are required to have bending resistance and wear resistance that can withstand reuse.

On the other hand, since iron nails are relatively heavy, when a large number of nails are used, not only the workers are burdened but also the building itself can be burdened. In addition, when rust occurs at the nail portion due to dew condensation, it causes corrosion not only of the nail but also of the lumber to be joined.

JP-A-9-3573

By the way, in recent years, industrial pure titanium, which is lightweight and has excellent corrosion resistance, has been used as building materials such as roofing materials and exterior wall materials (see, for example, Patent Document 1), and is often used for repairing important cultural properties and the like. It is becoming to be done.

Therefore, the present inventors came up with the idea of manufacturing a nail made of titanium, which is light in weight and excellent in corrosion resistance. However, titanium has the problem that its rigidity is about half that of iron and that it is easily worn. Therefore, when considering repeated use, titanium nails sometimes have problems in terms of bending resistance and wear resistance.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide a titanium nail excellent in bending resistance and wear resistance, and a titanium material used as the raw material thereof.

The present invention has been made to solve the above problems, and the gist thereof is the following titanium nail and titanium material.

(1) Made of industrial pure titanium or titanium alloy,
Having a hardened layer from the surface to a depth of 100 μm or more,
A nail made of titanium, wherein the difference between the Vickers hardness at a position 100 μm in the depth direction from the surface and the Vickers hardness at a position 1000 μm in the depth direction from the surface satisfies the following formula (i).
30≤HVS-HVB≤200 (i)
However, each symbol in the above formula (i) is defined as follows.
HVS: Vickers hardness (HV0.1) at a position of 100 μm in the depth direction from the surface
HVB: Vickers hardness (HV0.1) at a position of 1000 μm in the depth direction from the surface

(2) The chemical composition of the industrially pure titanium or titanium alloy is, in mass %,
Fe: 1.5% or less,
Cr: 1.5% or less,
Ni: 1.5% or less,
O: 0.25% or less,
N: 0.05% or less,
C: 0.10% or less,
H: 0.015% or less,
balance: Ti and impurities,
The titanium nail according to (1) above, which satisfies the following formula (ii).
Fe+Cr+Ni≦1.5 (ii)
However, each element symbol in the above formula represents the content (% by mass) of each element contained in industrially pure titanium or titanium alloy, and is zero when not contained.

(3) the chemical composition, instead of a part of the Ti, is mass %,
Al: 2.0% or less,
Si: 0.5% or less,
Sn: 2.0% or less,
Zr: 3.0% or less,
Cu: 1.8% or less,
Nb: 1.0% or less,
V: 2.0% or less,
Mo: 2.0% or less,
Mn: 1.0% or less,
Co: 1.0% or less,
Pd: 0.25% or less, and Ru: 0.25% or less,
The titanium nail according to (2) above, containing at least one selected from the group consisting of:

(4) The titanium nail according to any one of (1) to (3) above, which is a Japanese nail.

(5) A titanium material used as a material for the titanium nail according to any one of (1) to (4) above,
Made of industrial pure titanium or titanium alloy,
0.2% proof stress at room temperature is 215 MPa or more,
Tensile strength is 340 to 510 MPa,
A titanium material having an elongation of 23% or more.

According to the present invention, it is possible to obtain a titanium nail excellent in bending resistance and wear resistance, and a titanium material used as the raw material thereof.

FIG. 1 is a diagram schematically showing a cured layer. FIG. 2 is a diagram schematically showing the shape of a Japanese nail. FIG. 3 is a diagram schematically showing a case where the shape of the head is the beginning of the roll and a case where the shape is a fold.

The inventors of the present invention conducted various studies in order to ensure bending resistance and wear resistance in titanium nails. As a result, it was found that hot forging after heating in an oxidizing environment is effective, and that the surface layer of a titanium nail can be hardened by forging after oxidizing the surface layer. By appropriately hardening the surface layer, it has become possible to improve the bending resistance and wear resistance of titanium nails to a level that poses no practical problems when repeatedly used.

An embodiment of the present invention has been made based on the above findings. Each requirement of this embodiment will be described in detail below.

1. Construction of Titanium Nail The nail according to the present embodiment is made of industrially pure titanium or a titanium alloy, that is, a titanium nail. Industrially pure titanium is a titanium material that does not contain intentionally added elements and is composed of impurities and Ti, and usually has a Ti content of 98% by mass or more.

As general industrial pure titanium, JIS Classes 1 to 4 or ASTM/ASME Grades 1 to 4 are exemplified. Typical impurity elements of industrial pure titanium are C, H, O, N and Fe.

A titanium alloy is an alloy containing 70% by mass or more of Ti. Examples of titanium alloys include α-type titanium alloys, α+β-type titanium alloys, and β-type titanium alloys. Examples of α-type titanium alloys include highly corrosion-resistant alloys (JIS Classes 11 to 13, 17, 19 to 22, and ASTM Grades 7, 11, 13, 14, 17, 30, and 31. and titanium alloys containing a small amount of various elements), Ti-0.5Cu, Ti-1.0Cu, Ti-1.0Cu-0.5Nb, Ti-1.0Cu-1.0Sn- 0.3Si-0.25Nb and the like.

Examples of α+β type titanium alloys include Ti-3Al-2.5V, Ti-5Al-1Fe and Ti-6Al-4V. Examples of β-type titanium alloys include Ti-11.5Mo-6Zr-4.5Sn, Ti-8V-3Al-6Cr-4Mo-4Zr, Ti-13V-11Cr-3Al, Ti-15V-3Al-3Cr-3Sn. , Ti-20V-4Al-1Sn, Ti-22V-4Al and the like.

1-1. Chemical Composition of Industrial Pure Titanium or Titanium Alloy Although the chemical composition of the industrial pure titanium or titanium alloy is not particularly limited, for example, the following elements can be contained within the composition range described below. . The reasons for limiting each element are as follows. Moreover, "%" about content in the following description means "mass %."

Fe: 1.5% or less Fe is a β-phase stabilizing element and has the effect of improving the tensile strength. Moreover, it also has the effect of increasing the β phase and improving the hot workability. However, when Fe is contained excessively, segregation tends to occur, which may result in deterioration of properties and susceptibility to cracking. Therefore, the Fe content is preferably 1.5% or less, more preferably 1.3% or less. On the other hand, although the lower limit is not particularly limited, the Fe content is preferably 0.02% or more, more preferably 0.03% or more, from the industrial purity of raw materials.

Cr: 1.5% or less Cr, like Fe, has the effect of improving tensile strength and hot workability. However, if Cr is contained excessively, segregation tends to occur, resulting in reduced ductility and cracking. Therefore, the Cr content is preferably 1.5% or less, more preferably 1.3% or less. On the other hand, although the lower limit is not particularly limited, the Cr content is preferably 0.003% or more, more preferably 0.004% or more, from the industrial purity of raw materials.

Ni: 1.5% or less Ni, like Fe and Cr, has the effect of improving tensile strength and hot workability. However, if Ni is contained excessively, segregation tends to occur, resulting in reduced ductility and cracking. Therefore, the Ni content is preferably 1.5% or less, more preferably 1.3% or less. On the other hand, although the lower limit is not particularly limited, the Ni content is preferably 0.003% or more, more preferably 0.004% or more, from the viewpoint of industrial purity of raw materials.

Moreover, when Fe, Cr, and Ni are contained in a composite manner as described above, the total content thereof preferably satisfies the following formula (ii).
Fe+Cr+Ni≦1.5 (ii)
However, each element symbol in the above formula represents the content (% by mass) of each element contained in industrially pure titanium or titanium alloy, and is zero when not contained.

This is because if the total content of Fe, Cr, and Ni exceeds 1.5%, segregation tends to occur and properties such as ductility tend to deteriorate. Therefore, the left-side value of formula (ii), which is the total content of Fe, Cr, and Ni, is preferably 1.5 or less. (ii) The left-side value of the formula is more preferably 1.3 or less, more preferably 1.25 or less. Although the lower limit of the left-side value of the formula (ii) is not particularly limited, it is preferably 0.03 or more, for example.

O: 0.25% or less O has the effect of improving the tensile strength. However, if O is contained excessively, the ductility may be lowered and cracks may easily occur. Therefore, the O content is preferably 0.25% or less, more preferably 0.2% or less. Thus, the O content can also be adjusted to obtain the desired strength. On the other hand, if the O content is excessively reduced, the manufacturing cost of the raw materials and the like increases, so the O content is preferably 0.03% or more.

N: 0.05% or less N is an impurity element contained in industrial pure titanium or titanium alloy. An excessive N content lowers ductility and makes cracks more likely to occur. Therefore, the N content is preferably 0.05% or less, more preferably 0.03% or less. It is preferable to reduce N as much as possible, but if N is excessively reduced, the manufacturing cost increases. Therefore, the N content is preferably 0.001% or more.

C: 0.10% or less C is an impurity element contained in industrial pure titanium or titanium alloy. Excessive C content lowers ductility and toughness, making cracks more likely to occur. Therefore, the C content is preferably 0.10% or less, more preferably 0.05% or less. It is preferable to reduce C as much as possible, but if C is excessively reduced, the manufacturing cost increases. Therefore, the C content is preferably 0.001% or more.

H: 0.015% or less H is an impurity element contained in industrial pure titanium or titanium alloy. If H is contained excessively, the ductility is lowered and cracks are likely to occur. Therefore, the H content is preferably 0.015% or less, more preferably 0.010% or less. It is preferable to reduce H as much as possible, but if H is excessively reduced, the manufacturing cost increases. Therefore, the H content is preferably 0.001% or more.

In addition to the above elements, one or more selected from the group consisting of Al, Si, Sn, Zr, Cu, Nb, V, Mo, Mn, Co, Pd, and Ru are contained within the ranges shown below. may The reason for limiting each element will be explained.

Al: 2.0% or less Al has the effect of improving the tensile strength. Therefore, it may be contained as necessary. However, if Al is contained excessively, the properties may deteriorate and cracks may easily occur. Therefore, the Al content is preferably 2.0% or less. The Al content is more preferably 1.5% or less. On the other hand, in order to obtain the above effects, the Al content is preferably 0.1% or more.

Si: 0.5% or less Si has the effect of improving oxidation resistance and strength. Therefore, it may be contained as necessary. However, when Si is contained excessively, segregation tends to occur, resulting in deterioration of properties and cracking. Therefore, the Si content is preferably 0.5% or less. The Si content is more preferably 0.3% or less. On the other hand, in order to obtain the above effects, the Si content is preferably 0.05% or more.

Sn: 2.0% or less Sn has the effect of improving the strength. Therefore, it may be contained as necessary. However, if Sn is contained excessively, cracks may easily occur. Therefore, the Sn content is preferably 2.0% or less. The Sn content is more preferably 1.5% or less. On the other hand, in order to obtain the above effects, the Sn content is preferably 0.1% or more.

Zr: 3.0% or less Zr has the effect of improving oxidation resistance and strength. Therefore, it may be contained as necessary. However, if Zr is contained excessively, cracks may easily occur. Therefore, the Zr content is preferably 3.0% or less. The Zr content is more preferably 2.0% or less. On the other hand, in order to obtain the above effects, the Zr content is preferably 0.1% or more.

Cu: 1.8% or less Cu has the effect of improving the strength. Therefore, it may be contained as necessary. However, when Cu is contained excessively, segregation tends to occur, and as a result, cracks may easily occur. Therefore, the Cu content is preferably 1.8% or less. The Cu content is more preferably 1.5% or less. On the other hand, in order to obtain the above effects, the Cu content is preferably 0.1% or more.

Nb: 1.0% or less Nb has the effect of improving oxidation resistance. Therefore, it may be contained as necessary. However, an excessive Nb content increases the manufacturing cost. Therefore, the Nb content is preferably 1.0% or less. The Nb content is more preferably 0.5% or less. On the other hand, in order to obtain the above effects, the Nb content is preferably 0.1% or more.

V: 2.0% or less V has the effect of improving the strength. Therefore, it may be contained as necessary. However, when V is contained excessively, cracks may easily occur. Therefore, the V content is preferably 2.0% or less. The V content is more preferably 1.0% or less. On the other hand, in order to obtain the above effects, the V content is preferably 0.1% or more.

Mo: 2.0% or less Mo has the effect of improving corrosion resistance. Therefore, it may be contained as necessary. However, when Mo is contained excessively, segregation tends to occur, and as a result, cracks may easily occur. Therefore, the Mo content is preferably 2.0% or less. More preferably, the Mo content is 1.0% or less. On the other hand, in order to obtain the above effects, the Mo content is preferably 0.1% or more.

Mn: 1.0% or less Mn has the effect of improving the tensile strength. However, when Mn is contained excessively, segregation tends to occur, resulting in reduced ductility and cracking. Therefore, the Mn content is preferably 1.0% or less. More preferably, the Mn content is 0.5% or less. On the other hand, in order to obtain the above effects, the Mn content is preferably 0.1% or more.

Co: 1.0% or less Co has the effect of improving tensile strength and corrosion resistance. However, if Co is contained excessively, segregation tends to occur, resulting in reduced ductility and cracking. Therefore, the Co content is preferably 1.0% or less. The Co content is more preferably 0.5% or less. On the other hand, in order to obtain the above effects, the Co content is preferably 0.1% or more.

Pd: 0.25% or less Pd has the effect of improving corrosion resistance. Therefore, it may be contained as necessary. However, excessive Pd content increases manufacturing costs. Therefore, the Pd content is preferably 0.25% or less. The Pd content is more preferably 0.2% or less. On the other hand, in order to obtain the above effects, the Pd content is preferably 0.04% or more.

Ru: 0.25% or less Ru, like Pd, has the effect of improving corrosion resistance. Therefore, it may be contained as necessary. However, an excessive Ru content increases the manufacturing cost. Therefore, the Ru content is preferably 0.25% or less. More preferably, the Ru content is 0.2% or less. On the other hand, in order to obtain the above effects, the Ru content is preferably 0.04% or more.

In the above chemical composition, the balance is Ti and impurities. Here, the term "impurities" refers to components other than the above that are mixed in by various factors in the manufacturing process, such as raw materials such as ores and scraps, during the industrial production of industrially pure titanium or titanium alloys. It means a permissible amount within a range that does not adversely affect the form, and a total amount of 0.5% or less is a level without problems.

Note that the above chemical composition is the average chemical composition of the interior of 1 mm or more in the depth direction from the surface. The content of each element may be measured by an inert gas fusion infrared absorption method, an inert gas fusion thermal conductivity method, a high frequency combustion infrared absorption method, or an inductively coupled plasma (ICP) emission analysis method.

2. Hardening Layer The titanium nail of this embodiment has a hardening layer 1 as shown in FIG. The hardened layer 1 exists from the surface to a depth of 100 μm or more. That is, the thickness of the cured layer 1 is at least 100 μm, and may be greater. If the thickness of the hardened layer is excessive, embrittlement tends to occur. Therefore, the thickness of the hardened layer is preferably less than 1000 μm, more preferably 600 μm or less, and even more preferably 300 μm or less. .

The hardened layer is a portion hardened as a result of oxidation caused by solid solution of oxygen from the surface. By forming a hardened layer near the surface layer, it is possible to increase the yield strength near the surface layer to which higher bending stress than the inside is applied. As a result, plastic deformation is less likely to occur, the rigidity of the nail as a whole increases, and the bending resistance improves. In addition, wear resistance is also improved. The portion deeper than the hardened layer 1 is, for example, as shown in FIG.

2-1. Hardness The hardened layer is harder than the base material having the properties of the titanium material, which will be described later. For this reason, the Vickers hardness at a position of 100 μm in the depth direction from the surface (hereinafter also referred to as “100 μm depth position”) and the position of 1000 μm in the depth direction from the surface (hereinafter also referred to as “1000 μm depth position”) ) satisfies the following formula (i).

30≤HVS-HVB≤200 (i)
However, each symbol in the above formula (i) is defined as follows.
HVS: Vickers hardness (HV0.1) at a position of 100 μm in the depth direction from the surface
HVB: Vickers hardness (HV0.1) at a position of 1000 μm in the depth direction from the surface

When HVS-HVB, which is the difference between the Vickers hardness at a depth of 100 μm and the Vickers hardness at a depth of 1000 μm, is less than 30, a hardened layer with sufficient hardness is not formed, and bending resistance is not obtained. It is not possible to improve the durability and wear resistance. Therefore, HVS-HVB is set to 30 or more. HVS-HVB is preferably 50 or higher. On the other hand, if the HVS-HVB exceeds 200, the hardened layer becomes excessively hard, resulting in reduced toughness and ductility. As a result, cracks are likely to occur during manufacture of the nail, and manufacturability is reduced. Therefore, HVS-HVB is set to 200 or less. HVS-HVB is preferably 150 or less.

The Vickers hardness HVC of the shaft center of the nail is not particularly limited, but is preferably in the range of 110 to 200 (HV1). If the HVC is less than 110 (HV1), it will be difficult to obtain sufficient strength as a nail. Therefore, HVC is preferably 110 (HV1) or more, more preferably 115 (HV1) or more. On the other hand, if the HVC exceeds 200 (HV1), it becomes difficult to work during hot working, making it difficult to obtain a desired shape. Therefore, HVC is preferably 200 (HV1) or less, more preferably 170 (HV1) or less.

For HVS, HVB and HVC described above, the hardness is measured with a micro Vickers tester at a depth of 100 μm, a depth of 1000 μm, and at the axial center. "HV0.1" is a hardness symbol when the test force is 0.9807 N (100 gf), and "HV1" is a hardness symbol when the test force is 9.807 N (1 kgf). HVS and HVB have a test force of 100 gf, and HVC has a test force of 1 kgf. The test force hardness is determined by a Vickers hardness test based on JIS Z 2244:2009.

For hardness measurement, 80% of the central portion of the total length of the nail, excluding 10% of the length from the head and 10% of the length from the tip, is used. The hardness test is performed by polishing the measurement surface of a test piece cut out so that the cross section parallel to the longitudinal direction passing through the axis of the nail serves as the measurement surface. Then, the hardness is measured at five points on each of three lines passing through the 100 μm depth position, the 1000 μm depth position, and the axial center portion. Let the average value of the hardness be the hardness of each position (HVS, HVB, and HVC).

3. Japanese nail The titanium nail of this embodiment can also be applied to a Japanese nail. Wakugi are nails that have been used in traditional architecture, wooden Japanese boats, brewing barrels and tubs, fixing fired roof tiles, etc. Wakugi is a nail whose product dimensions are specified in the unit of "sun" of the shakukan system and its auxiliary unit "min". Further, as shown in FIG. 2, the cross section of the trunk portion 4 located under the head portion 3 of the nail has a substantially rectangular shape, and the trunk portion tapers toward the tip. The cross section of the trunk portion 4 may be substantially circular. In the processing of the trunk portion 4, for example, the corner portions of the trunk portion 4 may be chamfered to form an R shape. Further, the corner portion of the trunk portion 4 may be chamfered or protruded. In addition, FIG. 3 shows a Japanese nail whose head shape is the winding head 7 or the fold 8. As shown in FIG.

In addition, as shown in FIG. 2, the long side of the cross section at the position of 1/10 of the length from the starting end 5 to the tip 6 from the starting end of the trunk (the boundary between the head and the trunk) 5 toward the tip 6 The ratio of the cross-sectional length (mm) of the trunk to the total length (mm) of the Japanese nail (hereinafter also referred to as "cross-sectional shape ratio"). ) preferably satisfies the following relationship: That is, when the total length of the Japanese nail is less than 1 sun 2 minutes (approximately 36 mm), the cross-sectional shape ratio is preferably in the range of 0.100 to 0.050. Moreover, when the total length of the Japanese nail is 1 sun 2 minutes (approximately 36 mm) or more, the cross-sectional shape ratio is preferably in the range of 0.035 to 0.065.

Also, Japanese nails preferably have a hammered pattern on the surface. A hammered pattern is a wavy pattern that continues at regular intervals, and the wavy portions have different sizes. As a result, unevenness with a depth of about 0.05 to 0.30 mm is formed. The small unevenness of the hammered pattern increases the coefficient of friction on the contact surface, reducing the possibility of loosening or falling off of the nail, which also helps prevent corrosion.

4. Titanium Material The titanium material used for the titanium nail of the present embodiment is preferably made of industrially pure titanium or a titanium alloy, which will also be described in the manufacturing method. Also, the 0.2% yield strength of the titanium material at room temperature is preferably 215 MPa or more. The tensile strength of the titanium material is preferably in the range of 340-510 MPa, and the elongation of the titanium material is preferably 23% or more. These characteristic values may be obtained by a tensile test conforming to JIS Z 2241:2011.

5. Manufacturing Method A preferable manufacturing method of the titanium nail according to the present embodiment will be described. The titanium nail according to this embodiment can be stably manufactured by, for example, the following manufacturing method.

A titanium material (industrial pure titanium or titanium alloy) is prepared as the material for the nail. The chemical composition of the titanium material is preferably within the range described above. Further, the titanium material is preferably a wire, and preferably has a 0.2% proof stress of 215 MPa or more at room temperature, a tensile strength of 340 to 510 MPa, and an elongation of 23% or more.

This titanium material is heated at a temperature of 800-920° C. in an oxidizing atmosphere. If the heating temperature is less than 800° C., the titanium material has a high deformation resistance, resulting in a decrease in manufacturability. Also, the hardened layer is not sufficiently formed. Therefore, the heating temperature is set to 800° C. or higher, preferably 820° C. or higher. On the other hand, if the heating temperature exceeds 920° C., the titanium material becomes too soft, making it rather difficult to shape the product. In addition, the formation of the hardened layer proceeds too much, resulting in an excessive thickness. Therefore, the heating temperature is set to 920° C. or lower, preferably 870° C. or lower.

The oxidizing atmosphere may be, for example, an air atmosphere. This is because if the atmosphere is not oxidizing, the surface of the titanium material will not be sufficiently oxidized, and the hardness and thickness of the hardened layer will be insufficient. As a result, it becomes difficult to obtain the desired bending resistance and wear resistance.

Also, the time for heating the titanium material, that is, the heating time is set to 3 to 30 minutes. This is because if the heating time is less than 3 minutes, the inside of the titanium material cannot be sufficiently heated. Therefore, the heating time is set to 3 minutes or longer. On the other hand, if the heating time exceeds 30 minutes, oxidation proceeds excessively and thick scales are formed. Therefore, the heating time is set to 30 minutes or less.

After the heating, hot forging is performed to form a predetermined nail shape. At this time, similarly, hot forging is performed in an oxidizing atmosphere. The method of molding into a predetermined shape is not particularly limited, but it is usually preferable to fabricate the head of the nail and then fabricate the body. Through such steps, the titanium nail according to this embodiment can be obtained. Barrel polishing or blasting may be performed to adjust the surface properties of the obtained nail. In addition, since the titanium nail of this embodiment has a hardened layer to obtain high bending resistance and wear resistance, the hardened layer on the surface must not be removed.

Hereinafter, the titanium nail according to the present invention will be described in more detail with reference to examples, but the present embodiment is not limited to these examples.

A titanium nail was manufactured using a titanium material having the chemical composition shown in Table 1. Table 1 also shows the tensile properties of the titanium material. A tensile test for examining tensile properties was performed in accordance with JIS Z 2241:2011.

The nail manufacturing conditions are as shown in Table 2. The heating time during production was 5 minutes. Here, in all the examples, the shape of the nail was a Japanese nail of 3.5 cm, the cross section of which was substantially rectangular, and the head part was either a fold or a top. In addition, No. Example No. 20 is an example in which barrel polishing was performed after hot working. Also, No. Example No. 23 is an example in which blasting was performed after hot working.

No. Example No. 22 is an example in which only cold working was performed. No. Example No. 24 is an example in which the cross section is slightly finished by hot forging, and after cooling, the surface is cut by a lathe at room temperature by about 1 mm. A hardness test, a bending test (bending test 1 and bending test 2), and an abrasion test were performed on the manufactured nail of each example according to the procedures described below.

(Hardness test)
A hardness test was performed in accordance with JIS Z 2244:2009 to measure HVS, HVB and HVC. A micro Vickers tester was used for the hardness test, and the test force was set to 0.9807 N (100 gf) for HVS and HVB. For HVC, the test force was 9.807 N (1 kgf). For the measurement, 80% of the central portion of the total length of the nail was used, excluding 10% of the length from the head and 10% of the length from the tip. The hardness test was carried out by polishing the measurement surface using a test piece cut out so that the cross section parallel to the longitudinal direction passing through the axis of the nail serves as the measurement surface. The hardness was measured at 5 points on each of three lines passing through the 100 μm depth position, the 1000 μm depth position, and the axial center, and the average value of the hardness was taken as the hardness at each position.

(Bend test 1)
Using an iron jig with a radius of curvature of 10 mm, the longitudinal center of the nail was bent by 20 degrees, and then the iron jig was removed to measure the degree of bending of each nail. As a reference piece, a piece obtained by cutting a titanium material symbol A into a cross-sectional shape equivalent to that of the shaft of a nail was used. The state of bending after the bending test was compared with that of the reference piece. When the bending was equal to or larger than that of the reference piece, it was evaluated as x, and when it was smaller than that of the reference piece, it was evaluated as ◯.

(Bend test 2)
In bending test 2, the test was performed using the same measurement method as in bending test 1, and as a reference piece, an iron SGD3 (JIS G 3108: 2021) cut into a cross-sectional shape equivalent to the shaft of a nail was used. . The tensile strength of SDG3 used is about 435 MPa. The state of bending of each nail after the bending test was compared with that of the reference piece. When the bending of each nail was larger than that of the reference piece, it was evaluated as x, and when it was equal to or smaller than that of the reference piece, it was evaluated as ◯.

(Abrasion test)
Using a marking pen whose tip tip is 1 mm in diameter and made of cemented carbide material G2, the surface of the nail was scratched multiple times, and the marks were visually observed. Specifically, the marker pen was held by hand and scratched 5 to 10 times with a length of about 2 to 5 mm as if writing letters. When the scratch mark was visually clearly visible, it was evaluated as ×, and when it was not clearly visible, it was evaluated as ○. Examples of ○ were evaluated as having good wear resistance. The results are also shown in Table 2 below.

No. 1 that satisfies the requirements of this embodiment. 1-21 had a hardened layer thickness of 100 μm or more and had good stiffness and wear resistance. On the other hand, No. 1, which does not satisfy the requirements of this embodiment. Nos. 22 to 24 were inferior in at least one of rigidity and wear resistance. No. With respect to No. 22, only cold working was carried out as is done when manufacturing nails by a conventional method, so oxygen did not dissolve from the surface, and the difference between HVS and HVB was small. No. In No. 23, the HVS-HVB difference was small because hot working was not performed in an oxidizing atmosphere. No. In No. 24, the surface was cut in the final process, so the hardened layer was lost and the difference between HVS and HVB became small.

The titanium nail of this embodiment is useful because it is lightweight and has excellent bending resistance, wear resistance and corrosion resistance. In particular, it is suitable for Japanese nails used in buildings such as important cultural properties.

1. Hardened layer 2 . Base material 3 . 4. head body 5 . 5. Beginning of body; tip 7 . Intro (head)
8. Fold (head)

Claims (5)

Made of industrial pure titanium or titanium alloy,
Having a hardened layer from the surface to a depth of 100 μm or more,
A nail made of titanium, wherein the difference between the Vickers hardness at a position 100 μm in the depth direction from the surface and the Vickers hardness at a position 1000 μm in the depth direction from the surface satisfies the following formula (i).
30≤HVS-HVB≤200 (i)
However, each symbol in the above formula (i) is defined as follows.
HVS: Vickers hardness (HV0.1) at a position of 100 μm in the depth direction from the surface
HVB: Vickers hardness (HV0.1) at a position of 1000 μm in the depth direction from the surface The chemical composition of the industrially pure titanium or titanium alloy is, in mass%,
Fe: 1.5% or less,
Cr: 1.5% or less,
Ni: 1.5% or less,
O: 0.25% or less,
N: 0.05% or less,
C: 0.10% or less,
H: 0.015% or less,
balance: Ti and impurities,
2. The titanium nail according to claim 1, which satisfies the following formula (ii).
Fe+Cr+Ni≦1.5 (ii)
However, each element symbol in the above formula represents the content (% by mass) of each element contained in industrially pure titanium or titanium alloy, and is zero when not contained. wherein the chemical composition, in place of part of the Ti, is in % by mass,
Al: 2.0% or less,
Si: 0.5% or less,
Sn: 2.0% or less,
Zr: 3.0% or less,
Cu: 1.8% or less,
Nb: 1.0% or less,
V: 2.0% or less,
Mo: 2.0% or less,
Mn: 1.0% or less,
Co: 1.0% or less,
Pd: 0.25% or less, and Ru: 0.25% or less,
3. The titanium nail of claim 2, containing one or more selected from the group consisting of: The titanium nail according to any one of claims 1 to 3, which is a Japanese nail. A titanium material used as a material for the titanium nail according to any one of claims 1 to 4,
Made of industrial pure titanium or titanium alloy,
0.2% proof stress at room temperature is 215 MPa or more,
Tensile strength is 340 to 510 MPa,
A titanium material having an elongation of 23% or more.

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